Automobile designers are today challenged by a broad range of requirements externally imposed by customer demands at one extreme and by government regulation at the other. One such customer demand is for the reduction of overall vehicle noise, vibration and harshness (NVH). Some vehicle owners prefer a quiet vehicle riding experience both within the vehicle cabin and under the engine hood. Other vehicle owners, particularly those who prefer sports cars and audible engine noise, do not want to entirely eliminate the resonance of a well-tuned engine and find that such engine noise actually enhances the driving experience. In response to the interests of the sports car enthusiast, the assignee of the instant patent application makes available induction soundtubes between the engine's air intake and the vehicle cabin to thereby provide the vehicle occupant and particularly the driver with some measure of vehicle feedback, particularly upon acceleration.
The engine-to-cabin induction soundtube is one example of how vehicle designers are enhancing the driving experience. Another example is the provision of an induction clean air tube between the engine's air induction system and the front fender of the vehicle where the tube acts as a fresh air inlet. However, adjusting vehicle engine noise to the satisfaction of the customer is not merely a matter of transmitting sound from the engine to another point on the vehicle. Instead, the soundtube arrangement must be acoustically tuned for specific engine frequencies. This is a task that introduces other challenges to vehicle designers given that the accelerating engine generates sound ranges through a number of harmonic orders with only a couple of orders representing desirable sounds.
Correct acoustical tuning of the engine air induction clean air tube is only one challenge faced by the vehicle manufacturer. Another challenge is to meet government air evaporative emission quality standards related to the release of hydrocarbons to the atmosphere. The engine is one source of vehicle evaporative emissions. These vehicle evaporative emission regulations require the control of polluting substances (primarily hydrocarbons) from the vehicle. As an example, fuel that is sprayed into the intake manifold by the fuel injector typically remains on the walls in the intake manifold and the intake valves after engine shut down, thereby allowing fuel vapor to flow out of the air induction system. The evaporative emissions in the form of escaping unburned fuel may exceed government mandated requirements for such emissions.
Government regulations have been expanded in recent years to regulate the hydrocarbon emissions from the vehicle even when the vehicle is unused and the engine is off. During such engine off soaks, the evaporative hydrocarbons may be emitted by the engine through the air induction system. These emissions are leaked from the vehicle from many sources including the air intake system. This is an expansion from prior rules in which only emissions from the fuel tank were captured typically using carbon-filled canisters. Government requirements now regulate the total amount of hydrocarbons any vehicle is permitted to emit to the atmosphere at all times. These captured substances need to be retained within the air induction system until the powertrain is again used when the retention system will purge and burn the hydrocarbons during engine combustion.
When the air induction system is a significant contributor to overall vehicle hydrocarbon levels, a hydrocarbon trap must be utilized to capture hydrocarbons during engine off and to release and burn hydrocarbons during normal engine operation. In addition, the engine air induction clean air tube pulls atmospheric air from the environment into the engine, thus potentially introducing particulates directly into the air induction system.
A vehicle application was encountered that required an opening into the vehicle fender cavity. This opening “transmitted” the tuned sound to the vehicle occupant but allows air flow into the engine air induction system. The additional air flow path required filtration of the air to the engine as well as a hydrocarbon control device.